If the windows are permanently closed, the concentration of carbon dioxide is increasing sharply inside the premises that leads to drowsiness, fatigueability, decrease of mental activity, migraine. Moreover, the airtight of plastic double-glazed units, which have replaced wooden window frames, causes the moisture balance upset. That creates an environment favourable to the appearance of mold or fungus. The frequent opening of the windows makes noise, dust, unpleasant odors, exhaust fumes, plant pollen in the flowering period and other allergens get inside.
